Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenue	$ 108,562	$ 97,483	$ 85,394	$ 84,868	$ 84,053	$ 84,536	$ 77,698	$ 77,221	$ 376,307	$ 323,508	$ 262,571
Operating expenses
Interchange and network fees									242,867	214,543	189,112
Other costs of services									44,237	40,314	28,798
Selling general and administrative									62,860	40,585	27,194
Depreciation and amortization									16,564	11,839	10,085
Change in fair value of contingent consideration									3,389	3,866	(218)
Income from operations	1,869	$ 1,194	$ (203)	$ 3,530	3,495	$ 2,923	$ 2,596	$ 3,347	6,390	12,361	7,600
Processing margin									106,866	83,180	56,759
Assets	349,302				175,142				349,302	175,142	139,991
Goodwill	168,284				83,954				168,284	83,954	58,517
Merchant Services
Segment Reporting Information [Line Items]
Revenue									336,800	302,929	248,005
Operating expenses
Interchange and network fees									236,170	209,695	185,141
Other costs of services									41,309	38,399	27,350
Selling general and administrative									25,150	23,291	13,858
Depreciation and amortization									11,788	9,535	8,029
Change in fair value of contingent consideration									51	1,772	192
Income from operations									22,332	20,237	13,435
Processing margin									76,343	68,811	47,389
Assets	203,326				141,977				203,326	141,977	113,568
Goodwill	108,472				69,666				108,472	69,666	49,173
Residual expense									17,022	13,976	11,875
Proprietary Software and Payments
Segment Reporting Information [Line Items]
Revenue									39,507	20,582	14,582
Operating expenses
Interchange and network fees									6,697	4,848	3,971
Other costs of services									2,928	1,916	1,559
Selling general and administrative									19,184	7,602	7,194
Depreciation and amortization									4,223	2,097	1,938
Change in fair value of contingent consideration									3,338	2,094	(410)
Income from operations									3,137	2,025	330
Processing margin									30,523	14,371	9,423
Assets	112,514				28,339				112,514	28,339	8,901
Goodwill	59,812				14,288				59,812	14,288	9,344
Residual expense									641	553	371
Other
Segment Reporting Information [Line Items]
Revenue									0	(3)	(16)
Operating expenses
Interchange and network fees									0	0	0
Other costs of services									0	(1)	(111)
Selling general and administrative									18,526	9,692	6,142
Depreciation and amortization									553	207	118
Change in fair value of contingent consideration									0	0	0
Income from operations									(19,079)	(9,901)	(6,165)
Processing margin									0	(2)	(53)
Assets	33,462				4,826				33,462	4,826	17,522
Goodwill	$ 0				$ 0				0	0	0
Residual expense									$ 0	$ 0	$ (148)